This invention relates to an exhaust gas recirculation (EGR) control system in an internal combustion engine, and more particularly to an EGR control system of the type associated with a control unit in which a required value of exhaust gas recirculation at a first predetermined engine temperature is previously memorized as a function of some engine operating parameters, which system is so arranged that exhaust gas recirculation is stopped when the engine temperature is below a second predetermined engine temperature which is lower than the first predetermined engine temperature.
In connection with a known EGR control system of the above-mentioned type, a required value of exhaust gas recirculation at a high engine coolant temperature such as 8.degree. C. is previously memorized in a control unit as a function of, for example, the pulse width for controlling fuel injection, which pulse width corresponding to an engine speed and an intake air amount. The engine coolant temperature is sensed by an engine coolant temperature sensor. Such EGR control system is so arranged that the exhaust gas recirculation is stopped when the engine coolant temperature is at a certain low level such as one below 35.degree. C., whereas the exhaust gas recirculation is carried out in the required value when the engine coolant temperature exceeds 35.degree. C.
In this regard, this EGR control system has encountered a problem in that exhaust gas recirculation in large amounts abruptly begins to be formed when the engine coolant temperature exceeds 35.degree. C. This causes combustion in the engine to deteriorate, which results in degradation in driveability of a motor vehicle on which the engine is amounted.